The present invention relates to a hydraulic screw tightening or tensioning device for tightening and loosening highly stressed screws or bolts.
Applicants' hydraulic threaded bolt tensioning devices known from DE 43 41 707 A1 and DE 196 38 901 A1 are comprised of a cylinder that is supported on a machine part that is to be clamped by a threaded bolt and a nut, at least one piston that is guided therein in a sealed manner, is periodically supplied with pressure, is supported on an extension of a change sleeve threaded onto a thread of the threaded bolt, and forms an annular chamber with the cylinder, and a pressure medium supply to the annular chamber.
The object of such screw tensioning devices is to apply a precisely prescribed tensioning force onto a screw in order to be able to tighten or loosen the nut that is threaded onto the screw. For this purpose, a change sleeve in the screw tensioning device is threaded onto the projecting thread above the nut, and thereafter the screw tensioning device is placed under hydraulic pressure. The result is that the screw is tensioned by extension. The forces thereby applied to the screw are extremely great, thus very greatly stressing the screw tensioning device and its components.
With these hydraulic screw tensioning devices: in particular the change sleeve is a highly stressed component that after a certain number of screw extensions, i.e. load changes, can fail in the region of the threaded end of the screw or bolt.
Since in such a case the entire system relaxes in an abrupt manner, the failed or broken-off part of the threaded sleeve, together with the piston and the cylinder, can be spun away with considerable energy, and significant damage to adjacent machine components can occur, and operators can be injured. To avoid this, a trapping or collection device for these parts of the screw tensioning device is provided in DE 43 41 707A1.
However, to avoid a failure of the change sleeve, and to prevent the load change that is absorbed by these parts from being exceeded up to a fatigue failure, the object of DE 196 38 901 A1 is to replace the parts that are endangered by fatigue failure before such fatigue failure can occur. For this purpose, provided on the hydraulic screw tensioning device is a load change counter that, by means of the periodic pressurization of the screw tensioning device, is advanced upon each actuation, whereby the counting of no-load or idle strokes is prevented in that the load change counter is advanced only above a prescribed pressure.
The known hydraulic screw tensioning devices have proven advantageous and can be designed to have single or multiple stages in order to apply the forces that are required for all current sizes of the threaded bolts in order to bring about a predetermined extension.
European patent application EP 0 200 459 A2 discloses a hydraulic screw tensioning device according to which a change sleeve that can be threaded onto the threaded bolt that is to be tensioned is provided with a collar having an inclined surface against which is supported an annular piston that is disposed on an annular change sleeve. The annular piston and an annular shoulder on a cylinder element interengage and are guided in a sealed manner against one another. The facing, pressurized surfaces of the annular piston and of the cylinder element are respectively angled off in the same direction, so that due to the pressurization, a very high, expanding bending moment acts upon these annular surfaces, whereby this bending moment can be counteracted only by an appropriately large dimensioning of the elements in order to prevent wear of the seals and on the surfaces that glide on one another. Since such hydraulic screw tensioning devices are often used on threaded bolts that are disposed close together, any enlargement of the dimensions in a radial direction is a drawback.
It is an object of the present invention to embody the components that are endangered by fatigue failure such that they can be subjected to a high number of load changes before fatigue failure can occur, in other words, that these highly stressed individual components can be used for a longer period of time before they have to be replaced. Furthermore, a screw tensioning device that is compact not only in diameter but also in length is to be made available, whereby the wear and tear of the piston and cylinder surfaces that slide against one another, as well as of the respective seals, is as low as possible.